Move almost all the code of this script into functions. There is no
intended behavior change. The goal of this commit is to make
subsequent improvements easier to follow.
A very large number of lines have been reintended. To see what's going
on, ignore whitespace differences (e.g. diff -w).
I followed the following rules:
* Minimize the amount of code that gets moved.
* Don't change anything to what gets executed or displayed.
* Almost all the code must end up in a function.
* One function does one thing. For most of the code, that's from one
"cleanup" to the next.
* The test sequence functions (run_XXX) are independent.
The change mostly amounts to putting chunks of code into a function
and calling the functions in order. A few test runs are conditional;
in those cases the conditional is around the function call.
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